"He was a victim of assault and a victim of homicide," Dina Shacknai told NBC News on Thursday. "Even though nothing will bring my only child Maxie back, I owe it to him, as his mother, to make sure the true facts of his death are known."

Dina Shacknai is at odds with the conclusion of Coronado police, who have called Max's death a tragic accident. Police say the boy fell over a railing and tumbled down the stairs at his father's historic John D. Spreckels mansion on July 11, 2011. He struck the carpeted floor face first, fracturing his forehead, police said. He was not breathing and did not have a pulse when paramedics found him. Max died a week later at Rady Children's Hospital in San Diego.

Dina Shacknai and the boy's father, Jonah Shacknai, a pharmaceutical company executive and multimillionaire, divorced in 2009, she said. She said they kept their relationship amicable, for the sake of their son.

"We believed in co-parenting and wanted the best for Maxie," Dina Shacknai said.

She said Max was visiting his father, spending time at the mansion to be with his two step-siblings, Jonah Shacknai's two children from a separate marriage. The older siblings, however, were not at the mansion at the time of Max's fall, she said.

She said the terrible set of events continue to shock and horrify her to this day.